If a journal has Grades set to No grades then the function journal_grades in http://moodle.cvs.sourceforge.net/moodle/moodle/mod/journal/lib.php should return NULL or false. Currently it returns an object with maxgrade set to 0 and grade set to NULL. This has the unwanted effect of making it show up in the gradebook.

Thus the lines 237 and 238 should be replaced by the single line

return NULL;